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  <title>ol-ext: Convex hull</title>
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    <h1>ol-ext: Convex hull</h1>
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  <div class="info">
    The <i>ol.coordinate.convexHull()</i> function calculate a <a href="https://en.wikipedia.org/wiki/Convex_hull">convex hull</a>
    or convex envelope, ie. the smallest polygon that contains all points of a set.
    <br/>
    It uses the <a href="https://en.wikipedia.org/wiki/Convex_hull_algorithms#Algorithms">Andrew's Monotone Chain Algorithm</a> to complete the hull.
    <p>
      It can be used to display a polygon <a href="map.cluster.convexhull.html">around the points of a cluster</a>.
    </p>
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  <!-- Map div -->
  <div id="map" style="width:600px; height:400px;"></div>
  
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    Click on the map to add features and calculate the convex hull.
    <ul><li>
        <button class="button" onclick="vector.getSource().clear();">Clear!</button>
    </li></ul>
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  <script type="text/javascript">

  // The map
  var map = new ol.Map({
    target: 'map',
    view: new ol.View({
      zoom: 4,
      center: [205461, 5867916]
    }),
    layers: [new ol.layer.Geoportail({ layer: 'GEOGRAPHICALGRIDSYSTEMS.PLANIGNV2' })]
  });

  // Add over interaction that draw hull in a layer
  var vector = new ol.layer.Vector({ source: new ol.source.Vector() })
  map.addLayer(vector);

  var draw = new ol.interaction.Draw({ source:vector.getSource(), type:"Point" });
  map.addInteraction(draw);

  var hull, pts;
  draw.on("drawend", function(e){
    if (!vector.getSource().getFeatures().length) {
      hull = new ol.Feature(new ol.geom.Polygon([[0,0]]));
      vector.getSource().addFeature(hull);
      pts = [];
    }
    pts.push(e.feature.getGeometry().getCoordinates());
    hull.setGeometry(new ol.geom.Polygon ( [ ol.coordinate.convexHull(pts) ] ));
  });

  </script>
  
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